1. Field of the Invention
The present invention relates generally to apparatus for the storage and transport of nuclear waste material, and, more particularly, to a nuclear waste storage canister and a cover therefor.
2. Description of the Prior Art
A commercial nuclear facility generates electrical power by converting heat energy into electrical energy. The heat energy is generated as a byproduct of fission of a nuclear fuel source in which the fission process is permitted to occur at a controlled rate. In a commercial nuclear power facility, the nuclear fuel source is positioned underwater in a reactor core area of the facility. Nuclear fission is permitted to occur at a controlled rate by appropriate physical spacing of the nuclear fuel, and by positioning of nuclear moderators amongst the fuel. The water in the reactor core is permitted to circulate in a heat transfer relationship with the nuclear fuel source, thereby allowing the heat energy generated during the nuclear fission to be transferred to the coolant water. The heated coolant water is utilized to heat a secondary water system which, in turn, operates steam generators in order to produce electrical energy.
The nuclear fuel which fuels the fission process is, in most instances, positioned in fuel rods, of which a plurality thereof are positioned in the reactor core to generate the heat energy. The fuel rods are hollow metal pipes, having lengths of up to 16 feet, which are filled with the nuclear fuel. The fuel rods are supported by a supportive structure such that the fuel rods are maintained in precisely spaced arrays. The fuel rods, together with the supportive structure, are referred to as a nuclear fuel assembly. The reactor core areas of most commercial nuclear power facilities are of sizes to allow greater than one hundred fuel assemblies to be positioned therewithin at any time. The fuel assemblies are maintained underwater, and the water circulates among the fuel assembly in a heat transfer relationship. Such quantities of fuel assemblies suitably positioned in a reactor core create amounts of heat to allow generation of commercially useful amounts of electrical energy.
Over time, the heat energy generated by the nuclear fuel contained in the fuel rods of the fuel assemblies decreases. When the heat energy generation of the nuclear fuel falls beneath a predetermined level, replacement of the "spent" fuel material is necessitated. During such occasions, the entire fuel assemblies are removed from the reactor core, and are replaced with fuel assemblies having fuel rods containing fresh nuclear fuel material. However, the fuel assemblies removed from the reactor core still contain residual amounts of nuclear fuel material. These fuel assemblies, therefore, still possess significant heat generative properties.
In order to prevent overheating of the spent fuel assemblies subsequent to their removal from the reactor core, the spent nuclear fuel assemblies are stored in an underwater storage area; such underwater storage area is frequently referred to as a spent fuel pit. The heat generated by the spent fuel assemblies is dissipated by the water circulating through the spent fuel pit.
To most efficiently utilize the space of existing spent fuel pits, various methods and apparatus have been developed in order to consolidate, or otherwise allow, greater amounts of spent fuel and other nuclear waste material to be stored within a given area.
For example, several methods and apparatus have been disclosed in the prior art for removing the fuel rods of a fuel rod assembly, and reconfiguring the fuel rods into an array in which the spacing between adjacent fuel rods is minimized. The supportive structure of the fuel assembly may then be crushed, dismantled, or otherwise compacted. Such methods allow the storage capacity of a spent fuel pit to be approximately doubled.
Once removed from the fuel assembly and reconfigured into a compacted array, the spent fuel rods are positioned within storage canisters. The storage canisters are of dimensions allowing the fuel rods from one or more fuel assemblies to be stored therein. The compacted supportive structures of the fuel assemblies may similarly be stored in the storage canisters.
The size, shape, and weight of the storage canisters are determined by the lengths of the fuel rods to be stored therein. Typically, however, the waste canisters are between 13 and 16 feet in length, and have cross sectional dimensions of six to nine inches square. A storage canister containing the fuel rods of two fuel assemblies is of a weight (including the weight of the fuel rods) of up to 4,000 pounds.
The storage canisters are constructed such that water is permitted to circulate amongst the material stored therein. The coolant water must additionally be allowed to drain from the canister when the canister is lifted out of the storage pool. Such design requirements are met by constructing the canisters so that their bottom ends are open. Water is thereby allowed to circulate through the interior of the canister. The open ends additionally prevent pressure differentials between the interior and exterior of the canister.
The storage canisters are positioned in desired arrangements and numbers in a spent fuel pit. Apparatus has also been disclosed in the prior art in order to aid in the support and positioning of the storage canisters.
Handling of the storage canisters in order to allow for their positioning and repositioning in the spent fuel pit requires use of an overhead crane, or the like, having a canister handling tool affixed thereto. In order to facilitate such handling, the storage canister contains some type of connection device to facilitate connection with a canister handling tool. A canister cover is oftentimes attached to an end of the storage canister to allow connection to a handling tool. In order for the canister cover to accommodate the largest possible payload, the cover must be securely affixed to the canister, while still allowing coolant water to circulate among the material stored in the canister.
It is, accordingly, an object of the present invention to provide apparatus for the storage of nuclear waste material.
It is a further object of the present invention to provide a storage canister construction and a canister cover therefor for the storage of nuclear waste material.